A conventional in-wheel motor drive device 101 is disclosed in Japanese Unexamined Patent Publication Laid-Open No. 2006-258289, for example. Referring to FIG. 10, the in-wheel motor drive device 101 includes a motor part 103 to generate driving force in a casing 102 mounted on a car body, a wheel hub bearing part 104 connected to a wheel, and a reducer part 105 to reduce rotation speed of the motor part 103 and transmit it to the wheel hub bearing part 104.
In the above in-wheel motor drive device 101, a low torque and high rotation motor is employed for the motor part 103 with a view to reducing the device in size. Meanwhile, the wheel hub bearing part 104 requires a high torque to drive the wheel. Thus, a cycloidal reducer which is compact in size and capable of obtaining a high reduction ratio is employed for the reducer part 105 in some cases.
In addition, the conventional reducer part 105 using the cycloidal reducer includes a motor side rotation member 106 having eccentric parts 106a and 106b, curved plates 107a and 107b arranged in the eccentric parts 106a and 106b, a rolling bearing 111 to rotatably support each of the curved plates 107a and 107b with respect to the motor side rotation member 106, a plurality of outer pins 108 to allow the curved plates 107a and 107b to generate rotation motion by engaging with periphery surfaces of the curved plates 107a and 107b, and a plurality of inner pins 109 to transmit the rotation motion of the curved plates 107a and 107b to a wheel side rotation member 110.
In the above in-wheel motor drive device 101, a lubricant oil is sealed in the reducer part 105, and supplied to contact parts between the curved plates 107a and 107b, and the outer pin 108 and the inner pin 109, and a track surface of the rolling bearing 111.
At this time, the lubricant oil becomes hot due to frictional loss of the reducer part 105, and an iron loss and agitation resistance of the motor part 103, so that its lubrication performance is lowered. As a result, durability of the in-wheel motor drive device 101 could be lowered.